1. Field of the Invention
This invention relates to an innovative sensor device for detecting the torque features of a driven electric screwer.
2. Description of Related Art
In the field of electric screwers sensor devices are well known for detecting the torque features of the electric screwer. Such devices are connected to the outlet of the electric screwer and normally comprise a current torque sensor and a rotation angle sensor the measuring of which, as is known, enables the suitable performance curves of the electric screwer to be plotted.
The torque sensor is made of a metal shaft that transmits the torque of the electric screwer and on which an extensometer is fixed, for example of resistive type. The angle sensor is formed by an encoder connected mechanically to the shaft.
In order to make the signal from the extensometer that rotates with the shaft reach the measuring and processing electronics sliding contacts are normally used that rest on suitable conductive rings arranged alongside one another on the peripheral surface of the rotating shaft.
A drawback of known devices is in the devising the encoder function. In fact, using a mechanical encoder introduces dragging torque that falsifies the measuring of the extensometers. In order to overcome the drawback, optical encoders have been suggested. Optical encoders, however, suffer from the effect of dust and other impurities. A large source of dust is in the sliding contacts of the extensometers.
A typical drawback of sliding contacts is that they produce dust (especially in the case of sliding surfaces made of graphite) because of the continuous sliding of the contacts. In the case of detecting devices for detecting the torque features of electric screwers, the dust produced by the contacts of the torque sensor may disturb the operation of the detecting encoder for detecting optical angular rotation. It is therefore generally necessary to use seal washers that insulate the containing chamber containing the sliding contacts on the side of the device containing the encoder. Such washers in turn cause friction that is additional to the rotation of the measuring shaft. Further, over time the washers harden, worsening shaft rotation friction, and thus losing the dustproof function.
A general object of the present invention is to overcome the drawbacks of the prior art by providing a detecting device for detecting torque features of an electric screwer that is insensitive to dust in a satisfactory manner and which enables the detecting errors of the torque sensors arising from friction between the supporting shaft of the extensometers and the encoder to be minimized.
Another drawback of the known sensors of the type mentioned above is that they have great electrical noise due to the jumps of the sliding contacts. On the other hand, the elastic force that pushes the contacts against the conductive rings cannot be increased to reduce the jumps, as this would have a consequent braking effect on the shaft that would disturb measuring. Especially if the friction introduced by the encoder is reduced, it becomes important to limit a braking action of the electrical contacts of the torque sensors.
A further object of the present invention is to overcome the aforesaid drawbacks by providing a device for detecting torque features of an electric screwer, that reduces the electrical noise caused by the sliding contacts, without having an unacceptable increase of the contact force.
A still further object is to have a device with reduced overall dimensions and improved inertia features.